In recent years, a navigation device capable of displaying, based on map information stored in an HDD or a DVD, a map of the neighborhood of the position of a user's vehicle or a map of the vicinity of a predetermined position, along with landmarks, traffic information, and the like on a display of the device is widely used. In such a navigation device, when a user sets a destination, a search is performed for an appropriate route to the destination and also the travel time for the travel is calculated, whereby it is possible to present the resultant information to the user.
In such a navigation device, a technique is proposed for displaying, on an optimal scale, a map which displays accessible positions, accessible in all directions from the current position within a time set by a user (see Patent Document 1, for example).
Further, in an accessible range displaying device used for a car allocation/command system of a taxi, a security company or the like, a technique is proposed for displaying a range accessible from the current position within a certain amount of time, by drawing a smooth curve around the range in an amoeba-like manner (see Patent Document 2, for example).    Patent Document 1: Japanese Patent Publication No. 3385657    Patent Document 2: Japanese Laid-Open Patent Publication No. 11-16094